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Abstract:

In order to achieve a steering feel for SbW systems and EPS systems
having a control design for controlling the steering torque by generating
a target steering torque (torTB) that can be adapted to various steering
systems, vehicle types, or requirements, in which the resulting steering
feel is a steering feel, in all driving conditions and driving
situations, which is equivalent to, or better than, hydraulic and
electromechanical steering systems available on the market today,
according to the invention: a base steering torque (torB) is determined
as a function of an externally acting force (torR) and a vehicle speed
(velV); a damping torque (torD) is determined as a function of a steering
speed (anvSW) and the vehicle speed (velV); a hysteresis torque (torF) is
determined as a function of the steering speed (anvSW) and the vehicle
speed (velV); a centering torque (torCF; torC) in the direction of the
straight-ahead position is determined as a function of a steering wheel
angle (angSW) and the vehicle speed (velV); and the base steering torque
(torB), the damping torque (torD), the hysteresis torque (torF) and the
centering torque (torCF; torC) form individual components, as a function
of which the target steering torque (torTB) is determined.

Claims:

1. A method for determining a target steering torque (torTB) for a
steering means of a steering device in a vehicle, comprising: a base
steering torque (torB) is determined as a function of an externally
acting force (torR) and a vehicle speed (velV); a damping torque (torD)
is determined as a function of a steering speed (anvSW) and the vehicle
speed (velV); a hysteresis torque (torF) is determined as a function of
the steering speed (anvSW) and the vehicle speed (velV); a centering
torque (torCF; torC) in the direction of the straight-ahead position is
determined as a function of a steering wheel angle (angSW) and the
vehicle speed (velV); and the base steering torque (torB), the damping
torque (torD), the hysteresis torque (torF) and the centering torque
(torCF; torC) form individual components, as a function of which the
target steering torque (torTB) is determined.

2. A method according to claim 1, wherein the hysteresis torque (torF)
and/or the damping torque (torD) are additionally determined as a
function of a steering torque (torSW).

3. A method according to claim 1, wherein the base steering torque (torB)
is determined by means of predefinable characteristic base steering
torque curves, with characteristic base steering torque curves having
various progressions being provided for at least two different speed
ranges.

4. A method according to claim 1, wherein the centering torque (torCF;
torC) is generated in a predefinable angular range around the
straight-ahead position.

5. A method according to claim 1, wherein the externally acting force
(torR) corresponds to a toothed rack force and/or a cornering force.

6. A method according to claim 1, wherein a return torque (torAR) is
determined as a function of the steering wheel angle (angSW), the vehicle
speed (velV) and the steering speed (anvSW), and serves as a further
individual component.

7. A method according to claim 6, wherein the return torque (torAR) is
additionally determined as a function of a steering torque (torSW).

8. A method according to claim 1, wherein, in an intermediate step, a
base steering torque with self-alignment (torBC) is determined as a
function of the base steering torque (torB) and the centering torque
(torC), and the target steering torque (torTB) is found as a function of
the base steering torque with self-alignment (torBC), the damping torque
(torD) and the hysteresis torque (torF).

9. A method according to claim 7, wherein a target steering wheel speed
(anvSWS) is determined as a function of the vehicle speed (velV) and the
steering wheel angle (angSW), and the base steering torque with
self-alignment (torBC) is additionally determined as a function of the
target steering wheel speed (anvSWS), the steering wheel angle (angSW)
and the steering speed (anvSW), with a switch taking place from the base
steering torque (torB) to an undamped self-alignment torque (torC), when
a detected actual steering speed (anvSW) is lower than the predefinable
target steering wheel speed (anvSWS) and the base steering torque (torB)
is less than the originally required self-alignment torque (torC).

10. A method according to claim 1, wherein the portion of the
contribution of at least one individual component to the target steering
torque (torTB) can be predefined.

11. A method according to claim 10, wherein the portions of the
contributions of the individual components to the target steering torque
(torTB) are automatically predefined as a function of a predefinable
driving mode.

12. A method according to claim 10, wherein the portions of the
contributions of the individual components to the target steering torque
(torTB) are automatically predefined as a function of a current driving
condition.

13. A method according to claim 1, wherein at least one further moment is
determined and added to the target steering torque (torTB), the at least
one further moment representing at least one of the following: a tire
condition; a condition of a roadway surface; an unevenness of the
roadway; and a current driving condition, in particular oversteering or
understeering.

14. A method according to claim 1, wherein at least one further moment is
determined and added to the target steering torque (torTB), the at least
one further moment describing vibrating of the steering means to indicate
a hazardous situation or displaying advice for a recommended steering
direction.

15. A controller for controlling a steering device in a vehicle, wherein
the controller comprises a functionality for determining a target
steering torque (torB) for a steering means of the steering device, and
wherein by means of the functionality: a base steering torque (torB) can
be determined as a function of an externally acting force (torR) and a
vehicle speed (velV); a damping torque (torD) can be determined as a
function of a steering speed (anvSW) and the vehicle speed (velV); a
hysteresis torque (torF) can be determined as a function of the steering
speed (anvSW) and the vehicle speed (velV); a centering torque (torCF:
torC) in the direction of the straight-ahead position can be determined
as a function of a steering wheel angle (angSW) and the vehicle speed
(velV); and the base steering torque (torB), the damping torque (torD),
the hysteresis torque (torF) and the centering torque (torCF; torC) form
individual components, as a function of which the target steering torque
(torTB) can be determined.

16. A controller according to claim 15, wherein the controller is
designed to carry out a method according to claim 1.

17. A computer program, which can be executed on a controller for
controlling a steering device, wherein the computer program is programmed
to carry out a method according to claim 1.

18. A computer program according to claim 17, wherein the computer
program is stored on a memory element.

19. A computer program according to claim 17, for controlling the
steering device on a microprocessor in the controller.

20. A method according to claim 11, wherein the portions of the
contributions of the individual components to the target steering torque
(torTB) are automatically predefined as a function of a current driving
condition.

Description:

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for determining a target steering
torque for a steering means of a steering device in a vehicle.

[0002] The invention also relates to a controller for controlling a
steering device in a vehicle. The invention further relates to a computer
program that can be executed on a controller for controlling a steering
device in a vehicle.

[0003] In modern steering devices, for example in an electric power
steering (EPS) system or in what is referred to as a Steer-by-Wire (SbW)
steering system, a target steering torque is determined, which is applied
to a steering means, such as a steering wheel, in order to counteract the
force applied by the driver or support the force applied by the driver.
The target steering torque can also be referred to as the target manual
torque. This is intended to convey a driving experience to the driver
that corresponds to the current driving situation. In a conventional
steering system, in which a mechanical connection exists between the
steering means and the wheels to be steered, the target steering torque
decisively depends on cornering forces that act on the steering device,
and ultimately on the steering means, via a steering linkage.

[0004] In SbW steering systems, the target steering torque is generated,
for example, by means of a suitable steering wheel actuator. In an EPS
system, in which a mechanical connection exists between the steering
wheel and the wheels to be steered, modern control designs allow a target
steering torque that corresponds to the target manual torque to be
established so as to generate a desired steering feel at the steering
wheel. To this end, an electric motor, or an electromechanical servo
unit, is actuated or adjusted so that the target steering torque is set
in accordance with the desired target manual torque. The target steering
torque can specify the torque at the torsion bar, or the torque at the
steering wheel.

[0005] Various approaches exist for calculating the target manual torque,
or for calculating the target steering torque, for both SbW systems and
for EPS systems having a control design for controlling the steering
torque. Depending on the type of the steering system, the steering torque
corresponds, for example, to the manual torque and/or to what is referred
to as the torsion bar torque. The aforementioned approaches are based on
various application functions; however, when combined, they do not convey
a satisfactory steering feel in some driving conditions, or in some
driving situations. For example, the current transverse acceleration, in
the form of the toothed rack force, can be taken into consideration in
determining the target steering torque. In addition, further variables
may be included. Moreover, existing application functions can be
included, which take into consideration, for example, additional moments
of friction, so that the effect of the transverse acceleration actually
experienced at the steering means can be represented more realistically.

[0006] In principle, determining the target steering torque first entails
the problem of selecting suitable input variables. These input variables
can then be combined in a variety of ways, such that the influence of an
individual input variable is frequently no longer fully traceable, and
thus it is difficult to correct or improve the target steering torque.

SUMMARY OF THE INVENTION

[0007] It is the object of the present invention to achieve a steering
feel, both for SbW systems and for EPS systems having a control design
for controlling the steering torque, by generating a target steering
torque. The steering feel, or the target steering torque, must be
adaptable to various steering systems, vehicle types, or requirements.
The resulting steering feel must be a steering feel that is equivalent
to, or better than, hydraulic and electromechanical steering systems
available on the market today, in all driving conditions and driving
situations. This is intended to provide the driver with reliable and
precise information, to as great an extent as possible, on current
driving conditions and driving situations by way of the target steering
torque and by way of the steering means.

[0008] The object is achieved by a method of the type mentioned above, by
finding the target steering torque as a function of individual
components, with the individual components comprising at least one base
steering torque, a damping torque, a hysteresis torque and a centering
torque. These individual components can be combined into the target
steering torque, for example by way of addition.

[0009] The base steering torque is determined as a function of an
externally acting force, this being, for example, the toothed rack force,
or a transverse acceleration determined by means of a suitable sensor,
and as a function of a vehicle speed. The base steering torque thus
generates a base steering force level, in which the current toothed rack
force is taken into consideration as a function of the current speed. The
base steering force level is preferably generated by characteristic
torque curves that can be applied and are dependent on the toothed rack
force. There exist various progressions of the characteristic base
steering torque curves for various speeds. These various progressions of
the characteristic base steering torque curves can be determined, for
example, as a function of a certain vehicle, or a comfort level or a
steering feel to be achieved. The base steering torque can be used to
achieve what is referred to as the servotronic effect known from
hydraulic steering systems. According to a different embodiment, the base
steering torque is generated by means of a characteristic map, whereby
the base steering torque is determined as a function of a current vehicle
speed and a current externally acting force.

[0010] The damping torque is determined as a function of a steering speed,
such as a steering wheel speed, and the vehicle speed. This generates
active damping, which allows the driver to be assisted in the steering
process, for example by stabilizing the steering. For this purpose, it
may be possible to specify a higher steering torque for a high vehicle
speed and a high steering speed so as to reduce the risk of oversteering.

[0011] The hysteresis torque is determined as a function of the current
steering speed and the current vehicle speed. The hysteresis torque
opposes the steering wheel movement and thus allows friction to be
represented. The hysteresis torque is advantageously additionally
determined as a function of a current steering torque, whereby the
steering experience is improved even further.

[0012] The centering torque is determined as a function of a steering
angle and the vehicle speed. The centering torque generates a steering
torque in the direction of the straight-ahead position of the steering
means, whereby an improved steering feel is achieved. Given the
dependence on the vehicle speed, the centering torque can, for example,
be raised at high vehicle speeds and reduced at low vehicle speeds. The
centering torque is preferably generated so that it depends on a
predefinable angular range around the straight-ahead position. As a
result, this allows a minor deviation from the straight-ahead position to
be easily signaled by way of the contribution to the target steering
torque, whereas it can be assumed that a major deviation from the
straight-ahead position does not require a particular contribution of the
centering torque to the target steering torque because the greater
deviation is being sufficiently signaled by other components.

[0013] The method according to the invention thus allows precise
determination of individual moments that are intended to contribute to
the target steering torque. Moreover, the contribution of each individual
components can be adapted particularly well to various steering systems,
vehicle types or desired steering feels. To this end, it is particularly
advantageous if the contribution of at least one individual component can
be applied. This can be achieved, for example, by multiplying each
individual component by a factor that can be predefined for this
individual component, and by then adding the products thus obtained to
the target steering torque. This allows, for example, a component to be
entirely suppressed (factor=0) so as to determine a fault, or undesirable
behavior, particularly easily and reliably in the determination of the
target steering torque. Moreover, the contribution of each component can
be amplified (factor>1) or diminished (factor<1). In this way, an
application can be executed particularly well, because the influence of
the individual components on the entire target steering torque can be
predefined or controlled. This further makes it possible to automatically
predefine the contributions of the individual components in accordance
with a predefinable driving mode. For example, if a rather "spirited"
driving mode is desired, the contribution of individual components to the
target steering torque can be adapted accordingly. A spirited driving
mode can differ from a luxurious driving mode, for example, by
transmitting more information about the current transverse acceleration
to the driver in the spirited driving mode.

[0014] According to an improved embodiment, a return torque is determined
as a function of the steering angle, the vehicle speed and the steering
speed and serves as a further individual component. The return torque
brings about what is referred to as an active return by generating a
steering torque in the direction of the straight-ahead position, so that
a target steering speed that is dependent on the steering angle and the
vehicle speed is established. Depending on the steering speed, a steering
torque component is restoring or damping. This enables even further
improved self-alignment.

[0015] According to another preferred embodiment, first a base steering
torque with self-alignment is determined as a function of the base
steering torque and the centering torque in an intermediate step. Then
the target steering torque is found as a function of the base steering
torque with self-alignment and the damping torque and hysteresis torque.
Moreover, a target steering wheel speed is preferably determined as a
function of the vehicle speed and the steering angle, and the base
steering torque with self-alignment is additionally determined as a
function of the target steering wheel speed that is determined, the
steering angle and the steering speed.

[0016] This embodiment implements a quasi-static steering force level
solely by way of the base steering torque. Given the dependence on the
steering rack force or on the externally acting force, the base steering
torque already generates a return behavior that is comparable to the
return of a conventional hydraulic steering system. However, to attain
improved return behavior and generate an improved target steering torque,
a self-alignment torque and a damping torque are taken into
consideration, analogously to the aforementioned active return.

[0017] A switch is preferably made from the base steering torque with
self-alignment to an undamped self-alignment torque, when a detected
actual steering speed is lower than a predefinable target steering speed
and when the base steering torque is less than the originally required
self-alignment torque. These conditions exist, for example, when the
driver takes their hands off the steering wheel while driving, and thus
does not transfer any moment to the steering system. This automatically
prompts a switch to an undamped self-alignment torque, which effects a
self-alignment of the steering into the straight-ahead position and
increases safety.

[0018] Advantageously at least one further moment is determined and added
to the target steering torque. The additional moment can be, for example,
information about the driving conditions, the tire conditions, or the
condition or type of the roadway surface. The moment can moreover be part
of a drive assist system, by means of which tracking or autonomous
driving is implemented. For example, a hazardous situation can be
indicated by vibrating the steering means, or advice for a recommended
steering direction can be displayed. Such moments are particularly
helpful for safely driving a vehicle and can be taken into consideration
and applied with particular ease by means of the method according to the
invention.

[0019] It is particularly important to implement the method according to
the invention in the form of a computer program, which can be executed on
a controller for controlling a steering unit in a vehicle, and notably on
a microprocessor in the controller, which is programmed to carry out the
method according to the invention. In this case, the invention is
implemented by the computer program, and thus this computer program
represents the invention in the same manner as the method does, the
computer program being programmed for the execution thereof. The computer
program is preferably stored in a memory element. The memory element used
can notably be an optical, electric or magnetic storage medium, for
example a random access memory, a read-only memory, a flash memory, a
hard drive, or a digital versatile disk (DVD).

[0020] The object is also achieved by a controller of the type mentioned
above that comprises the controller means for carrying out the method
according to the invention. These means are implemented, for example, in
the form of a computer program that is executed by the controller.

[0021] Additional characteristics, application options and advantages of
the present invention will be apparent from the following description of
exemplary embodiments of the invention, which will be described based on
the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a steering device comprising a controller according to
the invention;

[0023] FIG. 2 is a schematic block diagram of a functionality according to
the invention for determining a target steering torque according to a
first exemplary embodiment; and

[0024]FIG. 3 is a schematic block diagram of a functionality for
determining a target steering torque according to a second exemplary
embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] FIG. 1 shows a controller 1, which is associated with a steering
device 2. A microprocessor 3 is disposed in the controller 1 and is
connected via a data line 4, such as a bus system, to a memory element 5.
The controller 1 is connected, via a signal line 6, to a motor 7, such as
an electric motor, whereby the controller 1 can control the power of the
motor 7. The motor 7 acts on a torsion bar 9 via a transmission 8. A
steering means 10, such as a steering wheel, is disposed on the torsion
bar 9 and can be used to apply a torque to the torsion bar 9 as a result
of a driver actuating the steering means 10.

[0026] The steering device 2 moreover comprises a steering gear 11, which
is designed, for example, as a rack-and-pinion steering gear. The
steering gear can further be designed as a ball-and-nut gear or
recirculating-ball gear. The description hereafter primarily assumes a
rack-and-pinion steering gear--to the extent necessary--in which the
steering gear 11 comprises a pinion 12a and a toothed rack 12b. The
steering gear 11 is connected to the wheels 14, for example, by way of
the pinion 12a and the toothed rack 12b and by a steering linkage 13.

[0027] The steering device 2 further comprises a torque sensor 15 for
detecting a steering torque torSW and a sensor 16 for detecting a
steering wheel angle angSW. In the exemplary embodiment shown in FIG. 1,
the sensor 16 is associated with the motor 7, so that the sensor 16
detects a rotor angle of the motor 7. This angle corresponds to the
steering wheel angle angSW (potentially with the exception of a factor
that denotes a gear ratio) because the motor 7 cooperates with the
torsion bar 9, and thus with the steering means 10, via the transmission
8. The steering wheel angle angSW can also be detected by means of a
sensor that is associated with the steering means 10 or the torsion bar
9. The sensor 16 disposed on the motor 7, however, can achieve a higher
resolution by detecting the rotor angle.

[0028] The steering device 2 further comprises a sensor 17, which can be
used to determine a toothed rack force torR. The toothed rack force torR
corresponds to a transverse acceleration or a cornering force acting on
the toothed rack 12b by way of the wheels 14 and the steering linkage 13.
It would also be possible, of course, to determine the transverse
acceleration or toothed rack force torR using other known methods. The
toothed rack force torR is transmitted to the controller 1.

[0029] In an alternative embodiment, the toothed rack force torR is
estimated based on other variables. This estimation is also carried out,
for example, by means of the controller 1. In this case, it is, of
course, not necessary to detect the toothed rack force torR by means of
the sensor 17 and transmit a corresponding signal to the controller 1.

[0030] The steering torque torSW detected by the torque sensor 15 and the
steering wheel angle angSW detected by the sensor 16 are likewise
transmitted to the controller 1. Moreover, a current vehicle speed velV
is transmitted to the controller or calculated there based on other
variables. A steering speed anvSW is also supplied to the controller 1.
The steering speed anvSW denotes the rotational speed by which the
steering means 10, and thus the torsion bar 9, can be actuated. The
steering speed anvSW can be captured by way of a suitable sensor, for
example at the torsion bar 9. It is also possible for the steering speed
anvSW to be found by the controller 1, for example as a function of the
existing steering wheel angle angSW and the time.

[0031] The operating principle of the method for determining a target
steering torque which is executed in the controller 1 is shown based on
the block diagrams of exemplary embodiments in FIGS. 2 and 3. The method
is realized here in the form of a computer program, in which the
individual blocks, or the functionalities corresponding thereto, are
suitably implemented. The computer program is stored, for example, in the
memory element 5 and is executed on the microprocessor 3.

[0032] FIG. 2 shows a function 20, by means of which a base steering
torque torB is generated as a function of the toothed rack force torR and
the vehicle speed velV. The base torque represents a base steering force
level, which is determined, for example, by way of characteristic torque
curves that can be applied and that are dependent on the toothed rack
force torR. To this end, various progressions of the characteristic
torque curves for various speed ranges are stored in the function 20 or
are accessible to the function 20. This allows functions that are known
from hydraulic steering systems to be implemented. For example, it may be
provided that a higher base steering torque is generated at a higher
speed, whereby the servotronic effect known from hydraulic steering
systems is achieved.

[0033] Moreover, the use of the toothed rack force results in improved
feedback of information about the force conditions for the road-wheel
contact. In this way, feedback is implicitly provided for information
regarding a friction coefficient, the unevenness of the roadway surface,
or a current driving condition, such as understeering or oversteering,
for example.

[0034] In a function 21, a centering torque torCF is generated as a
function of the vehicle speed velV and the steering wheel angle angSW.
The centering torque torCF presents itself to the driver at the steering
wheel 10 as what is referred to as center point feeling. The centering
torque torCF ensures that a steering torque in the direction of the
straight-ahead position of the steering means 10 is generated as a
function of the current steering wheel angle angSW so as to improve the
steering feel around the straight-ahead position of the steering wheel.

[0035] In a function 22, what is referred to as active return torAR is
generated as a function of the steering wheel angle angSW, the vehicle
speed velV and the steering speed anvSW, with this active return
providing a steering torque in the direction of the straight-ahead
position of the steering wheel, whereby a target steering speed, which is
dependent on the steering wheel angle angSW and the vehicle speed velV,
is established. Depending on the actual steering speed anvSW, the moment
is restoring or damping.

[0036] In a function 23, a damping torque torD, or what is referred to as
active damping, is generated as a function of the steering speed anvSW
and the vehicle speed velV.

[0037] In a function 24, a hysteresis torque torF is generated as a
function of the steering torque torSW, the vehicle speed velV and the
steering speed anvSW. The hysteresis torque torF can also be referred to
as a moment of friction, because it emulates friction that counteracts
the steering wheel movement and the steering speed direction. In this
way, the steering feel that is achieved, for example in SbW systems,
comes close to that of conventional power steering, in which a mechanical
connection exists between the steering gear 11 and steering means 10.

[0038] The base steering torque torB, the centering torque torCF, the
self-alignment torque torAR, the damping torque torD and the hysteresis
torque torF are respectively conducted to an element 26 by one of the
elements 25_B, 25_CF, 25_AR, 25_D and 25_F. In the element 26, the
transmitted moments are superimposed, for example by way of addition,
thus generating the target steering torque torTB.

[0039] The value of the respective moments torB, torCF, torAR, torD and
torF can be reduced or amplified by means of the elements 25_B, 25_CF,
25_AR, 25_D and 25_F. The elements 25_B, 25_CF, 25_AR, 25_D and 25_F thus
implement the abovementioned factors that make it possible to set the
value of an individual moment torB, torCF, torAR, torD and torF, or the
contribution of an one or more moments torB, torCF, torAR, torD and torF
to the overall target steering torque torTB, to zero. This is
advantageous, for example, when a target manual feel or a target steering
torque torTB is applied to a particular vehicle. It is therefore
particularly easy to check which individual component is the cause of an
undesirable or faulty signal, and thus makes an undesirable or faulty
contribution to the target steering torque torTB. Undesirable or faulty
moments can develop in the system as a result of vibrations. This process
thus allows better adaptability of the entire functionality.

[0040] The elements 25_B, 25_CF, 25_AR, 25_ and 25_F also allow for easy
switching between various steering feels. For this purpose, the elements
25_B, 25_CF, 25_AR, 25_ and 25_F are parameterized, for example, so that,
by predefining parameters, various steering feels can be directly
implemented, for example by selection in a menu in the vehicle. This can
be achieved particularly easily if the parameters correspond to the
respective factors. According to an advantageous embodiment, at least one
parameter is automatically determined as a function of a current driving
condition.

[0041] In the exemplary embodiment shown in FIG. 2, a quasi-stationary
steering force level is obtained from the base steering torque torB, the
centering torque torCF and the active return or the return torque torAR.
In this exemplary embodiment, active steering wheel self-alignment in the
direction of the straight-ahead position is influenced not only by the
return torque torAR, but also by the centering moment of the centering
torque torCF. In addition, functional coupling exists between the return
torque torAR and the damping torque torD or the active damping, because
these two moments generate a damping torque as a function of the
respective application.

[0042] In order to make it even easier to apply the desired steering feel,
in the exemplary embodiment shown in FIG. 3, the moments influencing the
quasi-stationary steering force level are functionally decoupled. For
this purpose, in the exemplary embodiment shown in FIG. 3, in a function
30, first a base steering torque torB is generated, which corresponds to
the base steering torque torB shown in FIG. 2.

[0043] In a function 31, a target steering wheel speed anvSWS is generated
as a function of a current vehicle speed velV and a current steering
wheel angle angSW. The significance of the target steering wheel speed
anvSWS will be described in more detail hereafter in connection with
other functions.

[0044] In a function 32, a centering torque torF is generated as a
function of the current vehicle speed velV and the steering wheel angle
angSW. As with the centering torque torCF described in relation to 2,
this centering torque torC is a steering torque that acts in the
direction of the straight-ahead position of the steering wheel. The
centering torque torC, however, is primarily used as a centering or
self-alignment torque, while the centering torque torCF described in
relation to FIG. 2 is primarily used to generate a center point feeling.
The portion of the target steering torque torTB responsible for
self-alignment is implemented in the exemplary embodiment shown in FIG. 2
by means of the return torque torAR or the active return.

[0045] In a function 33, a damping torque torD is generated, which
corresponds to the damping torque torD represented by the function 23 in
FIG. 2. In a function 34, a hysteresis torque torF is generated, which
corresponds to the hysteresis torque torF represented in FIG. 2 and
generated by function 24.

[0046] The damping torque torD and the hysteresis torque torF are
conducted to a function 37 by elements 36_D and 36-F. The elements 36_D
and 36_F correspond to the elements 25_D and 25_F. As with the function
26, the function 37 is used to combine the individual moments that are
generated, and is achieved by way of addition, for example, whereby the
target steering torque torTB to be generated is obtained.

[0047] The moments torB and torC generated by the functions 30 and 32, and
the target steering wheel speed anvSWS generated by the function 31, are
supplied to a function 35. Using these moments and the steering wheel
angle angSW and the steering speed anvSW, the function 35 finds a base
steering torque with self-alignment torBC, which is supplied to the
function 37 via an element 36_BC. The element 36_BC acts analogously to
the elements 36_D and 36_F and consequently allows the contribution of
the base torque with self-alignment torBC to the target steering torque
torTB to be reduced, amplified or entirely eliminated.

[0048] The exemplary embodiment shown in FIG. 3 shows improved functional
decoupling of the individual application functions 30, 31, 32, 33 and 34
by first implementing the quasi-static steering force level by way of the
base steering torque torB. Given the dependence on the toothed rack force
torR, the base steering torque torB already generates a return behavior
that is comparable to the return of a conventional hydraulic steering
system. However, in the same manner as with the active return, or the
return moment torAR shown in FIG. 2, a self-alignment torque torC and a
damping torque torC are also required for improved return behavior.

[0049] By means of the function 35, a switch is made in the exemplary
embodiment shown in FIG. 3 from the base steering torque torB to an
undamped self-alignment torque, when the current steering speed anvSW is
lower than the applicable target steering speed anvSWS, and when the base
steering torque torB is less than the required self-alignment torque
torC. The switch behavior can, of course, likewise be adjusted, whereby
the functionality 35 can also be adapted to various vehicle types or
steering feels that are to be achieved.

[0050] The function 35 can be suitably parameterized for this purpose. In
addition, or simultaneously, the damping can be influenced or applied by
means of the function 33, and the damping torque torD generated by this
function 33, independently of a current steering force level and a
self-alignment torque.

[0051] In principle, existing known electromechanical steering systems
supply very little or no roadway feedback. Using the method or
application structures according to the present invention, improved
roadway feedback can be achieved. Because the information to be fed back,
for example a change in the cornering force, is contained in the toothed
rack force torR that is employed, this change in toothed rack force
results in a corresponding change in the base steering torque, which in
turn influences the target steering torque. A change in the cornering
force can result, for example, from a change in a friction coefficient,
an unevenness of the roadway, or during oversteering or understeering.
The power of the implied roadway or driving condition feedback depends on
the gradient of an applicable characteristic curve, by means of which the
base steering torque is determined.

[0052] As mentioned above, the present example employs the toothed rack
force torR on which the base steering torque torB depends. However, the
base steering torque torB can, of course, also be applied as a function
of another variable representing the cornering forces of the tires. A
suitable variable is, for example, the transverse acceleration instead of
the toothed rack force.

[0053] Using the proposed application structures, it is further
particularly easy to transmit additional information about the target
steering torque to the driver. For example, if a sudden change in the
toothed rack force torR is detected, prompt amplified feedback can be
provided so as to draw the attention of the driver to the drastic change.
To this end, for example, an amplification can take place as a function
of a current wheel speed, wherein at higher speeds the influence on the
target steering torque can be increased. The wheel speeds can be used to
detect or plausibilize interference, wherein a current difference in the
wheel speeds of various wheels can notably be used.

[0054] Using the proposed application structures, further moments can be
added with particular ease. For example, steering wheel rocking can be
added by way of simple addition, so as to point out a particular hazard
or prompt a driver, who may have become sleepy, to be attentive.

[0055] The proposed application structures can be implemented entirely
independently of the underlying steering system. While FIG. 1 shows an
electric rack-and-pinion steering gear, the proposed application
structures can also be employed in a SbW system. Here, the motor 7 is
then actuated, for example, so as to generate the manual steering torque
torTB, wherein an additional electric motor, which is not shown,
generates the actual steering torque, because no mechanical connection
exists between the steering wheel, or the steering means 10, and the
steering gear 11. The motor 7 can, of course, act on the torsion bar 9,
the toothed rack 12b, the steering gear 11 or the steering means 10 in
the known manner in various locations.